New data push back the origin of mammals by 20 million years

(ORDO NEWS) — After studying the structure of the teeth of the late Triassic animal, scientists came to the conclusion that the first mammals could have arisen on Earth 20 million years earlier than previously thought.

It is traditionally believed that the first representatives of our class – the so-called mammaliaforms , the closest relatives of modern mammals, differing from them only in tiny anatomical features – arose in the late Triassic period , about 205 million years ago.

Now, however, the current view of the time of the origin of mammals may be changing thanks to a new study of the dentition of the South American Brasilodon, which lived 225 million years ago, an animal that was previously considered a member of the cynodonts , the group from which mammals descended.

Because the key feature of modern mammals, the mammary glands, is not preserved in the fossil record, scientists in Brazil and the UK had to rely on other features of our class to determine if this animal was a mammal. One of these signs is diphyodont change of teeth , in which milk teeth are once replaced by permanent ones.

Having studied the dentition of the Brasilodon, scientists found that this animal had a change of teeth once. Permanent teeth were no longer replaced by new ones throughout life, as in cynodonts.

In other words, the structure of the teeth allowed scientists to unambiguously classify Brasilodon as a mammal, which means extending the lifetime of our class by as much as 20 million years.

New data push back the origin of mammals by 20 million years
Brasilodon’s teeth changed: after milk teeth ( dark brown ), permanent teeth ( yellow ), exactly like a modern mouse

It seems that the first mammals arose on Earth at about the same time as the first dinosaurs , and while reptiles were actively seizing a dominant position in ecosystems, our furry ancestors mastered a small size class, populating burrows and going hunting mainly at night.

This order of things was to be maintained for another 160 million years, until, with the end of the Mesozoic era, the distant descendants of the Brasilodon got a chance for world domination.

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